1. Field of the Invention
This invention relates to continuously variable speed transmission devices and, more specifically, to such variable speed transmission devices which include a mechanism for the transmission of power between grooved pulleys wherein the transmission mechanism includes at least one endless belt having a plurality of transverse rigid elements called links.
2. Description of the Prior Art
Numerous continuously variable speed transmission devices have been proposed, such as those described in U.S. Pat. No. 4,213,350 or French Patents Nos. 2,242,608 and 2,437,531 (Varitrac); French Patents Nos. 2,587,777 and 2,594,513 (Ford), 2,480,885 (Borg-Warner) or 2,414,664 (Guirriec); U.S. Pat. Nos. 4,338,081 (Nippondenso) and 4,340,378 (Gates Rubber); or International Patents Nos. WO 80/02060 (David & Ttard) or WO 84/04950 (Dayco); and numerous patents held by Van Doorne, such as, French Patent No. 2,089,587; U.S. Pat. Nos. 3,720,113 and 4,080,841; or European Patents Nos. 0,000,802, 0,014,013, 0,014,014, 0,014,492, 0,026,534 and 0,109,132.
There are different devices for the same application disclosed in European Patent No. 0,242,263 (Hutchinson) and French Patents Nos. 2,527,723, 2,536,486 and 2,536,487, or European Patent No. 0,109,556 (Michelin).
The majority of the inventions described in the above-mentioned patents, with the exception of those in the Hutchinson, Dayco and Michelin patents, use flexible connecting elements comprising metal bands and generally metal transverse links. Oil lubrication is required for the connecting elements to compensate for friction, and it is not uncommon to use special steels and employ very close tolerances, such as those found in the Van Doorne transmissions.
The devices of the prior art are often noisy, because the links tend to collide with one another at the entrance to or at the exit from the grooved pulleys or even in the sections of the belt between the pulleys. As a result, after several hours of use, there is significant wear of the endless belt and the links which can result in a misalignment of the transverse links and a poor operation of the entire apparatus.
In some double-belt systems, such as those described in European Patents Nos. 0,014,013 and 0,109,132 (Van Doorne) or WO 84/04950 (Dayco), it has been considered necessary to employ complex devices to keep the endless belts from escaping from the grooves of the links. Numerous shapes of links or tangent plates are utilized in continuously variable transmissions as evidenced by those described in U.S. Pat. Nos. 4,338,081 (Nippondenso) and 4,080,841 (Van Doorne); in French Patents Nos. 2,527,723, 2,536,486 and 2,536,487 (Michelin); and, in particular, in European Patents Nos. 0,000,802, 0,014,013, 0,014,492, 0,026,534 and 0,109,132 (Van Doorne). All of the tangent plates described in these documents include cross sections which are essentially trapezoidal and employ at least one groove in which at least one endless belt is engaged.
One of the problems most frequently encountered in this type of transmission by tangent plates rests in the guidance of these tangent plates at the entrance to and exit from the grooved pulleys. Accordingly, the prior art devices are often directed to such problems and, therefore, relate to means for holding the belt in the grooves and for guiding the transverse links relative to one another.
In order to keep the endless belt and the transverse links from coming apart, in the above-referenced patent held by Hutchinson, it is suggested that the transverse links can be connected to the longitudinal framework by means of an elastomer compound.
In order to solve the guidance problems, it is recommended, in the above-referenced patents held by Michelin, to give the longitudinal belt and/or the links special shapes, which tend to complicate the formation and production of the overall apparatus.
Other solutions for the guidance problem have been proposed, including the provision of at least one projection on one of the faces of the transverse links and at least one recess on the opposite face, as generally described in the European Patent No. 0,014,492 (Van Doorne). While such a device is apparently effective because it makes possible the engagement of a projection on one transverse link in a corresponding recess on the contiguous transverse link, it has the disadvantage of complicating the assembly of the transverse links on the endless belt, as the various faces must be aligned.
As a result, it has been found that the solutions to the above-mentioned problems, as proposed in most of the prior art devices, appear to include various disadvantages. For example, some such devices require a complex lubrication system including filters and purification devices for the lubricant. Others include fabrication problems due to the requirement for close tolerances and/or the need to use special steels and, therefore, result in very high production costs. Finally, some of the prior art devices employ complex assemblies which are still not able to completely eliminate the risks of malfunction or failure of the transmission.
All of the above-mentioned patents are incorporated herein by reference as if the entire contents thereof were fully set forth herein.